[pmwiki-users] Merge after simultaneous edits does not work

[romat2]

When second user saves a page that has been simultaneously edited by
another user then the following message appears.

"The page you are editing has been modified since you started editing
it. The modifications have been merged into the text below, you may
want to verify the results of the merge before pressing save.
Conflicts the system couldn't resolve are bracketed by <<<<<<< and
>>>>>>>."

But the edit box is always empty. Are there any requirements for merge?

Roman

pmwiki 2.0.22, php 4.3.10, apache 2.0.52 on XP SP2